Helmets generally include a shell, liner, and retention system. The helmet shell provides protection from protruding objects and is often configured to spread the impact load across the footprint of the helmet. The helmet liner is generally made of a softer and lower density material than the helmet shell. The helmet liner is often configured such that, upon impact, the helmet liner at least partially absorbs the impact energy from the force of an impact. The helmet retention system is generally configured to retain the helmet on the head of the user.